Jsprit build route with delivery that has the time window 10:00-12:00, but endTime of activity is 12:04. What is interesting that this bug appear only in case when we set the number threads more then 1.@stefan we can provide the reproducible example. I can not post here because it based on real user locations. I Can send on private email

That is an expected behavior. In fact, this is an activity start time window which means that your activity can finish outside that window. Example: The time window is 10:00-12:00 and the activity duration is 10 minutes. If your activity starts at 11:55 then the endTime is 12:05.
In case you want to ensure that your activity endTime is always less than 12:00, and based on my previous example, you need to set a time window 10:00-11:50.